The present invention relates to a process for producing inorganic granules and to the use thereof for the coloring of building materials, particularly concrete, asphalt, plaster and mortar, and for the production of slurries and paints for the protection of buildings.
Cement- and lime-bonded building materials such as plaster, sand-lime brick, asbestos cement parts and concrete blocks, particularly roofing tiles and paving stones as well as quarry tiles, are generally colored with inorganic pigments if they are to be of colored form. Thus it is customary in the building materials industry to use iron oxides or iron oxide hydroxides as red, black, brown or yellow pigments, to use manganese oxides as brown-black pigments, to use chromium oxides as green pigments and to use titanium dioxides as white pigments. Other examples include the use of carbon blacks as black pigments, nickel or chromium rutiles as yellow pigments, spinels which contain cobalt as blue and green pigments, spinels which contain copper as black pigments and mixed crystals of barium sulphate and barium manganate as blue pigments.
For coloring building materials, the pigments are normally used in powder form. In their ground form they have the advantage of good dispersibility. Pigment powders such as these have to be dispersed completely uniformly within a short time in concrete, for example. The disadvantage of these fine powders is that they do not exhibit good flow behaviour and frequently cake together and form lumps on storage. Adding them in accurately metered amounts is thereby made difficult. Another disadvantage of powders is that they tend to form dust.
It is known that these disadvantages can be avoided during the pigmentation of concrete parts by using aqueous suspensions of pigments instead of dry pigment powders. The use of pastes or slurries of this type, which contain 30 to 70% pigment by weight, has only been accepted with reluctance. In particular, and depending on the distance between the site of manufacture and the site of use, the additional water content can result in considerably higher transport costs. Moreover, the large amount of water which is supplied in conjunction cannot be processed in every concrete formulation.
The major part of the building materials industry has therefore kept to the use of dry powders. The understanding that granules are less readily dispersible in concrete formulations has hitherto stood in the way of the use of pigments in the form of microgranules. Pigment agglomerates or granules which are difficult to disperse necessitate considerably longer mixing times. If the normal short mixing times which are customary in the building materials industry are employed, stippled effects, streaks or pockets of color are formed at the surface of the concrete as a result of poor pigment distribution. Moreover, the strength of color contained in the pigment cannot develop, so that higher contents of pigment have to be used to obtain the same intensity of color of the concrete part.
DE-C-3 619 363 (U.S. Pat. No. 4,946,505, Jungk) describes pigment granules for coloring concrete materials which substantially consist of pigment and one or more binder(s) which enhance the dispersibility of the pigment in concrete. The following are cited as binders which act as dispersing aids in concrete: alkylbenzene sulphonate, alkylnaphthalene sulphonate, lignosulphonate, sulphated polyglycol ethers, melamine-formaldehyde condensates, naphthalene-formaldehyde condensates, gluconic acid, salts of low molecular weight, partially esterified styrene-maleic anhydride copolymers, and copolymers of vinyl acetate and crotonic acid. The content of substances such as these in the pigment is preferably 2 to 6% by weight.
DE-C-4 119 667 (U.S. Pat. No. 5,215,583, Krockert et al) describes a process in which pigment granules are produced by spray-drying, using soluble salts of the first two main groups of the periodic table. This process can also be employed for the granulation of aqueous suspensions or pastes. However, in some cases additives, for example additions of binders, result in an increase in viscosity which has to be compensated for by the addition of water. However, the economic viability of spray granulation is thereby reduced, because more water has to be evaporated with respect to the solid.
U.S. Pat. No. 5,401,313 describes the production of pigments as powders and as granules from aqueous suspensions in two stages, by spray-drying with electrochemical and chemical modification of the surface. On account of its precipitation stage, this process can only be employed for very dilute pigment concentrations of less than 10% solids. This means that high energy costs are inevitably incurred for the spray-drying stage.
The use of phosphates or lignosulphonates--as is described in some of the documents cited above--particularly in higher concentrations when applied to concrete, results in effects which are in part unwanted, for example to a lengthening of the setting time of the concrete. Moreover, despite their dispersion-stabilizing properties which are due to their high charge density, silicates are not always suitable due to the formation of difficultly soluble compounds (due to carbonization) over the course of time. The time of dispersion to obtain a uniform coloration is thereby increased. In some cases the viscosity of the suspension is increased before atomisation by the addition of inorganic binders. Flowability then has to be established again by corresponding dilution. However, the drying costs are at the same time increased due to the increased amount of water to be. evaporated.